Roofing shingles come in two primary types. A first type is typically flat and is designed so that there is a generous amount of overlap between adjacent shingles to create weather resistant joints to help ensure weather tightness. This first, edge-overlapping type may be flexible, such as the common composition or asphalt shingle, or it may be rigid, such as slate or some concrete shingles. A second type of roofing shingle has interlocking edges to secure the edges to one another and to help create effectively weather resistant joints to provide the desired weather tightness. The interlocking edges of this second, edge-interlocking type may, for example, have generally U-shaped edges creating lap joints, may have standing seam type of interlocking edges, or may have batten seam type of interlocking edges, or a combination thereof. A great deal of research has gone into the design of these interlocking edges. Shingles may be secured to the roofing substrate using, for example, adhesives or mechanical devices such as clips, which engage the edges of the shingles, and roofing nails, which secure the clips and/or the shingle itself to the roofing substrate. ATAS International, Inc. of Allentown, Pa. manufactures various types of interlocking metal shingles, including shingles having interlocking edges along all four sides. Owens Corning of Toledo, Ohio also makes interlocking metal roofing panels sold under the trademark MiraVista®.
The widespread use of photovoltaic (PV) systems mounted to homes, businesses and factories is generally considered to be a desirable goal. Several factors are believed to be critical to the acceptance of PV systems, in particular by the individual homeowner. Primary among the factors are cost and aesthetics. One way of addressing both cost and aesthetics has been through the use of photovoltaic shingle assemblies. One way such shingle assemblies address the cost issue is by being used as a replacement for conventional shingles, preferably using similar mounting techniques. The aesthetic issue has begun to be addressed by the use of photovoltaic assemblies in the form of shingles or roofing tiles having similar configurations and dimensions as conventional shingles or roofing tiles, and by the use of appropriate colors and reflecting characteristics to help provide an aesthetically pleasing visual appearance to the roof or other building surface. See, for example, U.S. Pat. No. 5,112,408. However, photovoltaic shingle systems have not been as widely accepted as hoped-for because 1) PV mounted integrally with the building roof as shingles operate at higher temperatures, causing a reduction in PV electrical output due to an inverse relationship between temperature and PV efficiency; 2) the same higher operating temperatures approach or exceed the upper limit of the warranted PV operating temperature (typically 80 degrees C.) and serve to shorten the useful life of the PV shingle; 3) some products call for electrical connections between shingles to be made under the roof deck, requiring holes to be drilled through the roof deck which increases the likelihood of water leaks; 4) there has been poor aesthetic match of PV shingles in conjunction with the non-PV areas of the roof; 5) some PV shingles have been limited to amorphous silicon PV technology, which suffer from a low operating efficiency; and 6) the value of the PV shingle has typically been limited to the electrical output of the PV plus the material value of displaced conventional shingles when the product displaces conventional shingles.
See U.S. Pat. Nos.: 3,769,091; 4,001,995; 4,040,867; 4,189,881; 4,321,416; 5,232,518; 5,575,861; 5,590,495; 5,968,287; 5,990,414; 6,061,978; and 6,111,189. See also EP1035591A1; and WO96/24013.